Molded pulp fiber containers are useful and popular for horticultural applications, such as the propagation of cuttings or seedlings, or as receptacles for flowers, plants or trees. Often plants are germinated or started in containers in a controlled environment and later transplanted. Also, plants are moved, within a container, from one ground site to another. One advantage of molded pulp containers in these types of uses is the fact that, over time, they will degrade in the ground. A plant started in a pulp container may later be transplanted to a different location in the ground or to another container, and the plant roots eventually penetrate through the container into the surrounding medium. Plastic horticultural trays, which do not degrade and are not root-penetrable, are undesirable to many users for this reason.
Molded pulp containers are disclosed in, for example, U.S. Pat. Nos. 2,858,647; 2,814,427; and 3,315,410. One type of product which is now in use comprises a tray-type horticultural container consisting of a number of detachable individual containers, each container being about 1 inch to 3 inches in size, wherein the tray has been molded as an integral unit.
In the greenhouse, in the germination environment, or in the ground, conditions exist which tend to prematurely degrade molded pulp and thereby cause a loss of structural strength in the container. Of course, eventual degradation of the pulp in the ground is desireable, but premature degradation in the greenhouse is preferably avoided. In the greenhouse, for example, warm and moist conditions tend to favor microbial proliferation on horticultural containers. In soil, when a container is buried, moist and nutrient-rich conditions similarly tend to promote microbial growth. In each of these environments, the pulp container is often soaked to full saturation. It is desirable, however, to maintain the structural integrity of the container in these conditions over extended time periods prior to permanent planting or retail potting, normally from 1-8 weeks, in order to facilitate handling and transplanting of the container contents.
Several approaches have been pursued in the prior art to improve the strength of molded pulp containers under greenhouse or soil burial conditions by preventing premature decomposition. One approach has been to thicken the walls and bottom of the container. This adds weight and bulk to the container, however, and does not avoid degradation to any significant extent. A different approach has been to design drainage ports into the container, with a view towards preventing water retention within the container interior. See, for example, U.S. Pat. No. 3,027,684. The most common approach, however, is to incorporate significant quantities of asphalt, such as bitumen, into the pulp fiber furnish to provide resistance against wetting in the final container. Molded pulp products which are currently available for horticulture normally contain between 10 and 30% by weight asphalt. Incorporation of such amounts of asphalt into the product molded pulp fiber container is advantageous in terms of improving the useful life of the container, but a number of disadvantages are associated with the use of asphalt. For example, asphalt is a costly component, and its use adds significantly to the cost of production. Also, the use of asphalt makes the manufacture of containers very heat-intensive, for the reason that when asphalt is added to a fiber furnish, it must be melted and flowed onto the fibers in order to be effective. In addition, any system to which asphalt is to be added must be set up as a separate stock system, white water system, machine and dryer. Further, the tackiness of the asphalt makes it difficult to mold an article having thin walls or complex shape. For these reasons, it would be desirable to eliminate, or reduce the amount of, asphalt from the molded pulp furnish yet retain satisfactory resistance against deterioration.
The prior art has recognized the benefit of incorporating a fungicide into pulp to prepare paper or paper products. U.S. Pat. No. 2,767,088 teaches the preparation of moldproof paper by the formation of an insoluble copper salt in the beater solution, which salt is said to be effectively retained by the paper fibers in the formed web. U.S. Pat. No. 2,858,647 teaches a pulp container prepared by adding a copper naphthenate solution to the pulp in the beater, which container resists decomposition in soil. Other patents showing paper having an antimicrobial agent incorporated therein includes U.S. Pat. Nos. 2,780,546; 2,204,066; 3,264,172; and U.K. Pat. No. 603,248.
It is noted that, due to environmental considerations and existing regulations, copper salts often cannot be used in molded pulp horticultural containers.
In the case of transplantable containers, it is desireable that the container be root-penetrable, so that the roots of a growing plant or seedling can penetrate the walls or bottom of the container and enter the surrounding medium after transplantation. Root penetration can be facilitated by providing openings such as holes or slots in the container. See, for example, U.S. Patent Nos. 3,785,088; 2,022,548 and 1,993,620. Another known means of providing root-penetrability is to form the container from a low-strength material, such as peat, which permits root penetration. See, e.g. U.S. Pat. Nos. 3,102,364; 2,728,169 and 3,187,463. Peat can be desireable for the reason that it tends to resist decomposition. In the art, peat has been used either alone or with paper pulp fibers present as a binder. Although peat is useful in a transplantable container in terms of its low burst strength properties and low tendency to degrade, use of peat adds difficulty and expense to the manufacturing operation. Peat pots also support mold and fungal growth under greenhouse conditions. Moreover, peat has a very low web-strength and cannot be easily shaped into small containers or containers of complex geometry. It would be desireable to provide a low burst strength, root-penetrable transplantable container which is not based on peat and contains little or no peat.
In current practice, many plants including flowering plants, agricultural crops and trees are germinated or started under carefully controlled conditions to assure optimal growth prior to transplanting. In large commercial operations, individual seeds are germinated and started in multi-cell plug propogation trays. These trays are typically made from plastic, for example polystyrene, and are not reused. The trays facilitate the transfer of the seedlings from one growth environment to another during different growth stages. These growth environments, like greenhouse conditions, are normally hot, humid and conducive to microbial proliferation. When the root system has sufficiently developed, the "plug" is mechanically or manually transferred to a retail pot or to the ground. It should be appreciated that this transfer step exposes the plant to potential transplant shock, and also requires that transfer be delayed until the root system of the seedling is relatively well-developed in the plug. Moreover, plastic is impermeable to gas and moisture, making these variables difficult to control when using a plastic propogation tray.
An alternative propogation system to plastic plug propogation trays are the solid transplantable media systems, such as compressed peat, Rock Wool, and the like. Although transplantable, these systems are not cost effective for many uses.